Generally, composite materials constitute a class of materials that provide for design flexibility by allowing their properties to be tailored according to the specific requirements for different applications. For example, metal matrix composites, such as aluminum matrix composites may be used for a variety of structural and non-structural applications, including applications for electronics, automotive and aerospace industries. Composite materials are generally classified on the basis of the shape and size of the reinforcements.
One type of composite material contains continuous fibers running along the length of the matrix. FIG. 2 shows a continuous fiber composite (10) made of a metal matrix (20) which is reinforced with ceramic fiber (30). FIG. 3 shows another type of composite material that has discontinuous ceramic fiber reinforcements. In the metal matrix composite (100) shown in FIG. 1, the particulate reinforcements (300) are intermetallics.
The properties of the composite materials are influenced by the matrix material as well as by the type, shape, size, and volume fraction of the reinforcing material. The main strengthening mechanism of continuous fiber composites is based on load transfer from the matrix to the fibers and the load is mainly carried by the fibers. The highest levels of strength and stiffness are attained using continuous fibers aligned in the direction of loading as the strong fibers carry the majority of the load. Although continuous fiber composites have superior strength in the direction of the fibers, their applications are limited by their high costs of production, the problems associated with their processing and their inferior transverse properties.
Generally, discontinuously reinforced composites are weaker than continuous fiber composites. However, discontinuously reinforced matrix composites are attractive for reasons such as their low cost, increased flexibility in processing and isotropy of mechanical properties.
For example, silicon carbide (SiC) is commonly used to manufacture discontinuously reinforced metal matrix composite materials. In particular, particulate composites of aluminum matrices with silicon carbide as the reinforcing material are commonly used. However, the load sharing by the silicon carbide particles is limited by the inherently weaker bond of the metal/ceramic systems.
There is need for a discontinuously reinforced metal matrix composite that has improved strength, stiffness and toughness and provides greater flexibility in processing. There is also a need for a processing method which allows for better processing control.